Gloss and smoothness are characteristics of a web of material that affect not only the appearance of the material but also its processability. For certain applications, high gloss and/or smoothness values are desired but they should also be as uniformly reproducible as possible.
At first the pressure in the roller gap was increased in order to increase the gloss and/or smoothness. However, this has the negative effect that the web of material is greatly compressed on the whole and thus suffers a loss of volume. In addition the web of material may also lose stability in this way. To prevent this disadvantage from becoming too serious, there was subsequently a trend toward increasing the temperature of the rollers that form the roller gap. This made it possible to further increase the gloss and smoothness but such a procedure is very energy intensive. In order to achieve roller temperatures of 200.degree. C., substantial quantities of energy must be supplied continuously because the rollers are constantly being cooled by the web of material passing by. In addition there have also been attempts to influence the gloss and smoothness through the moisture content of the web of material, but this has the disadvantage that the moisture supplied to the web must be removed again at least in part after the treatment, which entails additional process steps that increase the amount of time and equipment required for treatment of the web of material. Steam blasting tubes arranged between two roller gaps downstream from the deflection in a web of paper are known for influencing the moisture content when processing paper on supercalenders (U.S. Pat. No. 5,122,232). The steam emitted from the steam blasting tubes condenses in the ambient air and is deposited as a mist--for example, in the form of extremely fine water droplets--on the web of material. Another disadvantage of this procedure is that the entire vicinity around the web of material is then exposed to a very humid atmosphere that leads to corrosion of metal parts in the smoothing device.
This invention is therefore based on the problem of simplifying the method of improving the gloss and/or smoothness.